GPRS Tunneling Protocol (GTP), specified in 3GPP TS 36.413, is a group of IP-based communications protocols used to carry General Packet Radio Service (GPRS) within Global System for Mobile Communications (GSM), Universal Mobile Telecommunications Service (UMTS) and Long Term Evolution (LTE) networks. GTP can be decomposed into separate protocols, and GTP-U (GTP-User plane, specified in 3GPP TS 29.281) is one of these. GTP-U is used for carrying user data within the GPRS Core Network and between the Radio Access Network (RAN) and the core network.
As part of the GTP-U protocol, a GTP-U ERROR INDICATION message can be sent to notify a peer about faults on a specific bearer. The peer (the eNodeB) shall then upon reception of the error indication message initiate an E-RAB (E-UTRAN Radio Access Bearer) Release procedure.
FIG. 1 is a sequence diagram illustrating the above. A user equipment (UE) may have one or more links or bearers for enabling voice, video and/or data communication, e.g. Internet Protocol (IP) bearers. The UE is connected to the eNodeB (or eNB) over a wireless communication link. A serving gateway (S-GW) maintains data paths between the eNodeB and public data networks (PDN, not illustrated) and routes and forwards user data packets.
A Mobility Management Entity (MME) manages, inter alia, the access to network connections for the UE, the assignment of network resources, and mobility states to support paging, roaming and handovers. The MME controls all control plane functions related to subscriber and session management. The MME may manage thousands of eNodeBs.
If the serving gateway detects a fault on a specific bearer, it sends (arrow 1) an error message to the eNodeB. The eNodeB then initiates (arrow 2) the E-RAB release procedure for releasing the bearer. The E-RAB release procedure ends with a S1-AP ERAB RELEASE INDICATION message, that is sent (arrow 3b) to the MME, and also (arrow 3a) a user equipment context release message that is sent to the UE.